Sidelobe Amplitude Research Articles

Performance analysis of GFSK modulation over AWGN channel

This paper analyses the performance of Gaussian Frequency Shift Keying (GFSK) modulation in Additive White Gaussian Noise (AWGN) channels. Using MATLAB 2022b for simulations, the study explores GFSK modulation principles, the role of Gaussian low-pass filters, the characteristics reflected by Power Spectral Density (PSD), and the influence of Bit Time-Bandwidth Product (BT) on Bit Error Rate (BER). It has been observed that the Gaussian filter restricts sidelobe amplitudes and enhances spectral efficiency. Through varying BT values, it is observed that higher BT values correlate with lower BER. Additionally, the study successfully reconstructs original baseband signals through sampling decisions, confirming GFSK modulation effectiveness.

The Effect of Antenna Place Codes for Reducing Sidelobes of SIAR and Frequency Diverse Array Sensors

Synthetic impulse and aperture radar (SIAR) is a technique that frequency diverse array (FDA) radars can imply in practice, thus overcoming some of their challenges. SIAR radars, used in various fields like transportation and defense, can detect the range, azimuth angle, elevation angle, and Doppler of the target with their 4D‐matched filter and a single receiver. However, the challenge of high‐amplitude sidelobes is a significant concern for researchers. They have attempted to reduce it through various approaches, including frequency code, range–angle coupling, and range–Doppler coupling, to accurately identify target characteristics. This paper presents the antenna place code (AP code) parameter as a significant factor in minimizing sidelobe amplitudes. The parameter specifies that, rather than having all antennas active, a certain number of antennas are active in each pulse repetition interval (PRI) to achieve a lower sidelobe. Researchers have found that using AP codes can effectively lower the amplitude of the range–angle sidelobe, the range–Doppler sidelobe, error coupling, the repetition of sidelobe strands, and the output of angle error for different target angles. All studies are conducted on a linear array for simplicity. The output of various AP codes is compared to the previously common uniform array.

Phase-Optimized Multi-Step Phase Acoustic Metasurfaces for Arbitrary Multifocal Beamforming.

Focused ultrasound featuring non-destructive and high sensitivity has attracted widespread attention in biomedical and industrial evaluation. However, most traditional focusing techniques focus on the design and improvement of single-point focusing, neglecting the need to carry more dimensions of multifocal beams. Here we propose an automatic multifocal beamforming method, which is implemented using a four-step phase metasurface. The metasurface composed of four-step phases improves the transmission efficiency of acoustic waves as a matching layer and enhances the focusing efficiency at the target focal position. The change in the number of focused beams does not affect the full width at half maximum (FWHM), revealing the flexibility of the arbitrary multifocal beamforming method. Phase-optimized hybrid lenses reduce the sidelobe amplitude, and excellent agreement is observed between the simulation and experiments for triple-focusing beamforming metasurface lenses. The particle trapping experiment further validates the profile of the triple-focusing beam. The proposed hybrid lens can achieve flexible focusing in three dimensions (3D) and arbitrary multipoint, which may have potential prospects for biomedical imaging, acoustic tweezers, and brain neural modulation.

Four-element planar arrays focus a point-like source based on the artificial iterative phase conjugated processing

The artificial iterative phase conjugated processing is an improved algorithm of phase conjugation and has been proven to focus a sharp focal spot using linear array. Because cross-shaped four-element planar array and triangular four-element planar array are widely used in the situation of little acoustic measuring points , their focal patterns by the artificial iterative phase conjugated processing are discussed in this paper. Theory analysis and numerical simulations gives conclusions. Based on the artificial iterative phase conjugated processing, two arrays focus a smaller focal spot than that by phase conjugation. As their iterate number increases, focal spot size decreases but the sidelobe amplitude becomes big. Considering the focal spot size and sidelobe interference, the triangular four-element array has a clearer pattern than the cross-shaped one .

Focal spot enhanced by artificial iterative phase conjugated twin-line planar array

It has been proven that the artificial iterative phase conjugated linear array can enhance the focus. In this paper, twin-line planar array based on artificial iterative phase conjugated processing focuses a point-like source in a homogenous medium. Theory analysis and numerical simulations give conclusions. Contrasting with phase conjugation, artificial iterative phase conjugated twin-line planar array focuses a small focal spot and low sidelobes. Meanwhile, focal size and sidelobe amplitude decrease as iterate number increases. Furthermore, the focal spot size becomes sharp if the distance between the two linear array is larger than half a wavelength.

High-resolution mid-mantle imaging with multiple-taper SS-precursor estimates

SUMMARY SS-precursor imaging is used to image sharp interfaces within Earth’s mantle. Current SS-precursor techniques require tightly bandpassed signals (e.g. 0.02–0.05 Hz), limiting both vertical and horizontal resolutions. Higher frequency content would allow for the detection of finer structure in and around the mantle transition zone (MTZ). Here, we present a new SS-precursor deconvolution technique based on multiple-taper correlation (MTC). We show that applying MTC to SS-precursor deconvolution can increase the frequency cut-off up to 0.5 Hz, which potentially sharpens vertical resolution to ∼10 km. Furthermore, the high-pass frequency can be lowered (≪ 0.01 Hz), allowing more long-period energy to be included in the calculation, to better constrain the signal and reduce side lobes. Our method is benchmarked on full-waveform synthetic seismograms computed via AxiSEM3D for the PREM 1-D Earth model. We apply our novel MTC-SS-precursor deconvolution to ∼7000 seismograms recorded at broad-band borehole sensors of the Global Seismographic Network with source–receiver bounce points in the North-Central Pacific Ocean. The MTZ in this region appears to be thin, which agrees with previous results. We do not observe the 520-km discontinuity in our SS-precursor estimates. Additionally, we detect a low-velocity zone above the MTZ to the north of the Hawaiian Islands that has previously been inferred from asymmetry in side lobe amplitudes. Our high-frequency analysis demonstrates this feature to be a sharp interface (≤ 10-km thickness), rather than a thick wave speed gradient.

Power constraint waveform design based on ADMM algorithm for MIMO radar transmit beampattern

To address the problems of high sidelobe and large fluctuation amplitude of the mainside on matching the radar beampattern of multiple-input multiple-output (MIMO) radar, we proposed a transmission beampattern design method based on alternating direction method of multipliers (ADMM) under power limitation and peak-to-average ratio (PAR) constraint. The method used the Least-Most-Rule for the transmitting beamform design, i.e., the ratio of the maximum value of sidelobe to the minimum value of mainlobe as objective function. Meanwhile, the sum of power over the mainside and sidelobe is constrained to match the desired pattern. Then, the log-sum-exp function and Taylor's formula are used to approximate the optimization problem to produce a fourth-order polynomial on the beamform vector; finally, we introduce a dual variable and equation constraints and apply ADMM method to convert the fourth-order polynomial problem into the second-order polynomial problem for solution. In addition, the computational complexity of the proposed method is also analyzed. Two sets of experiments verify the effectiveness of the method in the simulation part.

Enhancement of the Unidirectional Radiation Pattern of Shear Horizontal Ultrasonic Waves Generated by Side-Shifted Periodic Permanent Magnets Electromagnetic Acoustic Transducers With Multiple Rows of Magnets

Shear horizontal (SH) guided waves are widely used in non-destructive evaluation and can be generated by permanent magnet electromagnetic acoustic transducer (PPM EMATs). PPM EMATs generate SH waves that propagate both forwards and backwards. This is often an undesirable characteristic. Unidirectional generation can be achieved by the interference mechanism produced by two independent sources. This, however, is non-feasible for the conventional PPM EMATs due to the arrangement of PPM array and racetrack coil. Recently, we presented a design of an SH EMAT with side-shifted PPM arrays that generates SH waves nominally in a single direction. Due to the shift of the produced wavefronts from each array, that design produced side-lobes in the backward semi-plane. In this paper, we enhance the unidirectional generation of SH waves with side-shifted PPM EMATs by evaluating the effect of the separation between individual arrays as well as the number of rows of magnets in each array. An analytical model is used to calculate the radiation pattern. The amplitude of the backward side-lobes decreases either with increasing the number of magnets rows or decreasing the lateral gap between rows. This behaviour is explained by the amount of wavefront misalignment introduced by each design. Increasing the number of magnets rows also increases the directivity and the energy of the forward generated waves. Twelve different configurations were fabricated, with a reasonably short wavelength of 12 mm, and experimentally evaluated, agreeing with the theoretically calculated radiation pattern. The magnitude of the backward side-lobes was roughly halved when compared with the original design.

Joint Optimization of Signal Waveforms and Filters for Long-Range MIMO Radars

This paper describes a new cyclic algorithm for minimization of signal sidelobes and crosstalk in multiple-input multiple-output (MIMO) radar. The designed algorithm, called SWAP by the authors, is suitable mainly for long-range radars, such as ground-based surveillance, approach, or weather radar. The minimization of energy or amplitude of side lobes, and crosstalk were used as the optimization criteria. The effect of the Doppler shift is also included in the optimization. Although the optimized signals do not maintain a strictly constant envelope, the peak-to-average power ratio (PAR) can be maintained below 1.7. This value is acceptable, especially for radars with modern transmitters based on GaN HEMTs. The algorithm allows for any arbitrary choice of elements weights, enabling the optimization of calculations for a wide range of applications. This paper also presents the results of algorithm testing under various conditions. The designed algorithm makes it possible to suppress the side lobes and crosstalk by up to 20 dB more than the matched filters. These results were achieved at the cost of a slight deterioration in signal-to-noise ratio (SNR) loss (less than 1 dB) and an increase in PAR (up to 2). The resolution of weak close targets is also slightly deteriorated. The algorithm converged quickly, and already after ten or 20 iterations, the results changed only minimally.

Critical Current Modulation in Josephson Junctions Contacted by Redundant Vias

We study the impact of redundant via placement on Fraunhofer interference patterns in superconductor–insulator–superconductor Josephson junctions with thin counter electrodes. By varying the number and location of contact vias to the counter electrode in otherwise equivalent junctions and studying the magnetic field dependence of the critical current, we observe a variety of unconventional features in the interference patterns, including a lifting of critical current minima and differences in node positions and side lobe amplitudes. We attribute these features to local changes in the Josephson phase gradient arising from the nonuniform magnetic thickness resulting from the vias. Our findings highlight the significant role that contact vias on thin counter electrodes play in the response of Josephson junctions to applied magnetic fields.

Voltage unbalance factor detection based Kaiser- maximum sidelobe decay convolution window and amplitude method

The wide application of distributed energy and nonlinear load causes the voltage unbalance of power grid. This paper establishes an accurate method based on the Kaiser- maximum sidelobe decay (K-MSD) convolution window and three-spectral line interpolated FFT algorithm and the amplitude method to detect the negative sequence voltage unbalance factor. The voltage fundamental wave amplitude is calculated by improved FFT algorithm, which improves the calculation accuracy. Then, the negative sequence voltage unbalance factor is calculated by the amplitude method. It avoids complex phasor calculations. Based on the proposed method the voltage unbalance factor detection system is developed and implemented in a platform. The simulation experiment results show that the proposed algorithm in this paper can effectively realize the accurate detection of unbalance factor under the interference of fundamental wave, harmonics and noise. Compared with the method recommended by the IEC61000-4-27, it is easy to implement and can achieve the same level of precision.

Piston Error Measurement for Segmented Telescopes with an Artificial Neural Network.

A piston error detection method is proposed based on the broadband intensity distribution on the image plane using a back-propagation (BP) artificial neural network. By setting a mask with a sparse circular clear multi-subaperture configuration in the exit pupil plane of a segmented telescope to fragment the pupil, the relation between the piston error of segments and amplitude of the modulation transfer function (MTF) sidelobes is strictly derived according to the Fourier optics principle. Then the BP artificial neural network is utilized to establish the mapping relation between them, where the amplitudes of the MTF sidelobes directly calculated from theoretical relationship and the introduced piston errors are used as inputs and outputs respectively to train the network. With the well trained-network, the piston errors are measured to a good precision using one in-focused broadband image without defocus division as input, and the capture range achieving the coherence length of the broadband light is available. Adequate simulations demonstrate the effectiveness and accuracy of the proposed method; the results show that the trained network has high measurement accuracy, wide detection range, quite good noise immunity and generalization ability. This method provides a feasible and easily implemented way to measure piston error and can simultaneously detect the multiple piston errors of the entire aperture of the segmented telescope.

A simple approach to nonstationary source waveform estimation in seismic records

A simple and practical method for source-waveform estimation from reflection seismic records is implemented by iterative identification of locally strongest reflections. Instead of conventional hypotheses about statistical properties of the whole records, the method is based on a general observation that stronger reflection peaks occur relatively sparsely and that smaller peaks adjacent to them are mutually incoherent. Tests with real well logs suggest that the subsurface often possesses such sparseness. Based on this property, the source waveform is obtained from seismic records by optimizing a combination of its practically important properties, such as the main-lobe width, side-lobe amplitudes, and phase character. Similarly, other types of optimization criteria can be used. The approach is stable with respect to noise and parameter variations and allows estimating the source waveforms without well-log control. By including inverse [Formula: see text]-filtering, time-variant amplitude scaling, and/or band-pass filtering, the approach allows correcting for reflection amplitude variations, nonstationarity due to seismic attenuation and dispersion, and also for coherent noise consisting in possible amplitude variations and phase shifts of the low- or high-frequency components of the records. By using the estimated source waveform, time-dependent waveforms and nonstationary wavelet matrices can be predicted at any reflection time. The method is illustrated by synthetic examples of logs with von Kármán distributions of velocity fluctuations and real well logs from an oil reservoir. In the synthetics, the spectral character and shape of the main lobe of the source waveform are reproduced well in all cases, and the phase character of the source is partly recovered when the subsurface reflectivity is dominated by reflections that are relatively sparse and strong compared to the adjacent reflectivity. In cases in which the phase of the source signal is unknown, the obtained waveforms are characterized by simple shapes with low-amplitude side lobes. Such waveforms are suitable for many applications from well ties and numerical modeling to deconvolution and [Formula: see text]-compensation.

A Novel Design and Implementation of FBMC Transceiver for Low Power Applications

The complex structure of the Filter Bank Multicarrier (FBMC) communication system is the main drawback affecting the performance of the system and causes a high-power consumption. The complexity arises from using a polyphase filter bank, which consists of fast Fourier Transform/ Inverse Fast Fourier Transform (FFT/IFFT) processors and a filter bank of Finite Impulse Response (FIR) filters. This paper presents the analysis and the implementation of a new design model for FBMC transceiver in which the polyphase filter is removed completely in both transmitter and receiver and uses instead of it, a multi-level cascaded structure of FIR subfilters. The coefficients of each subfilter selected using an optimization algorithm to minimize the amplitude of sidelobes compared to the amplitude of the main lobe in the frequency response of the subfilter. The proposed design reduces the number of multiplications compared to the conventional design by 65%. The field-programmable gate array (FPGA) implementation results indicate that the proposed architecture saves 24% of resources of the FPGA board, works faster, and saves 27% of power consumption compared to conventional FBMC transceiver.

A Novel Design and Implementation of FBMC Transceiver for Low Power Applications

The complex structure of the Filter Bank Multicarrier (FBMC) communication system is the main drawback affecting the performance of the system and causes a high-power consumption. The complexity arises from using a polyphase filter bank, which consists of fast Fourier Transform/ Inverse Fast Fourier Transform (FFT/IFFT) processors and a filter bank of Finite Impulse Response (FIR) filters. This paper presents the analysis and the implementation of a new design model for FBMC transceiver in which the polyphase filter is removed completely in both transmitter and receiver and uses instead of it, a multi-level cascaded structure of FIR subfilters. The coefficients of each subfilter selected using an optimization algorithm to minimize the amplitude of sidelobes compared to the amplitude of the main lobe in the frequency response of the subfilter. The proposed design reduces the number of multiplications compared to the conventional design by 65%. The field-programmable gate array (FPGA) implementation results indicate that the proposed architecture saves 24% of resources of the FPGA board, works faster, and saves 27% of power consumption compared to conventional FBMC transceiver.

Optimization of a spherical microphone array geometry for localizing acoustic sources using the generalized cross-correlation technique

Abstract Many workers are exposed daily to excessive noise levels. In order to reduce the noise exposure at the workstation, the main noise sources have to be detected. This task can be done with a microphone array and a source localization technique. Previous studies have shown promising results with time domain beamforming based on the generalized cross-correlation technique. The objective of this work is to propose an optimal spherical microphone array geometry dedicated to this technique. A cost function based on the symmetry of the aperture angle maps is proposed and is maximized using a Nonlinear Optimization by Mesh Adaptive Direct Search. Numerical results show that the optimized geometry improves the noise source map by reducing the side lobe amplitude without increasing the main lobe surface. Experimental measurements are carried out in a semi-anechoic chamber with prototyped spherical microphone arrays confirming that the optimized microphone array improves the quality of the noise source map.

On the use of modified phase transform weighting functions for acoustic imaging with the generalized cross correlation.

The generalized cross correlation (GCC) is an efficient technique for performing acoustic imaging. However, it suffers from important limitations such as a large main lobe width for noise sources with low frequency content or a high amplitude of side lobes for noise sources with high frequencies. Prefiltering operation of the microphone signals by a weighting function can be used to improve the acoustic image. In this work, two weighting functions based on PHAse Transform (PHAT) improvements are used. The first adds an exponent to the PHAT expression (ρ-PHAT), while the second adds the minimum value of the coherence function to the denominator (ρ-PHAT-C). Numerical acoustic images obtained with the GCC and those weighting functions are compared and quantitatively assessed thanks to a metric based on a covariance ellipse, which surrounds either the main lobe or the side lobes. The weighting function ρ-PHAT-C provides the smallest surface ellipses especially when the arithmetic of the GCC is replaced by the geometric mean (GEO). Experimental measurements are carried out in a hemi-anechoic room and a reverberant chamber where two loudspeakers were set in front of microphone array. The acoustic images obtained confirm that the ρ-PHAT-C with the GEO outperforms the GCC, GCC-PHAT, and GCC ρ-PHAT.

Excitation series design and pulse compression synthesis for high-resolution Lamb wave inspection

Lamb wave pulse compression is a promising technique for ultrasonic nondestructive evaluation and structural health monitoring, in which the excitation waveform is designed to exhibit attractive auto-correlation characteristics including short main-lobe width and small side-lobe amplitude. However, narrowing main-lobe will increase side-lobe amplitude, and vice versa. Conventional time windowing technique is a balance between main-lobe width and side-lobe amplitude. An improvement over time windowing is proposed using pulse compression synthesis method. In this method, a series of excitation waveforms are used to actuate Lamb waves, each response is processed by pulse compression, and all the compression signals are summed together. The excitation series are constructed as linear chirps weighted with different combinations of rectangular and Hanning window functions. The selection of the combination coefficients is optimized to ensure best signal summation. The effectiveness of the proposed method is demonstrated by an experiment, and the robustness to inaccuracy in dispersion compensation is also evaluated. Application of the proposed method for damage detection is demonstrated by a further experiment.

Low-Power Wideband Analog Channelization Filter Bank Using Passive Polyphase-FFT Techniques

Polyphase-FFT (P-FFT) techniques allow for low power implementations of high performance multi-channel filter banks by utilizing computation sharing like a standard fast Fourier transform (FFT). Additionally, it enables a longer “effective window length” than is possible in a standard FFT. This characteristic breaks the trade-off between the main-lobe width and the side-lobe amplitudes in normal finite impulse response filters. Thus, P-FFT techniques have been employed for the channelization of wideband input signals in high speed digital communication receivers. In this paper, we present a prototype analog P-FFT based filter bank in discrete time that is used to channelize wideband input signals so as to reduce the speed and dynamic range requirement of the ADCs. The four-channel I/Q prototype is implemented using TSMC’s 65 nm GP technology. Based on passive switches, the design operates at high speed, consumes low power, and offers high linearity performance. The measured transfer function shows >38 dB side-lobe suppression at 1 GS/s operation. The average measured IIP3 is +25 dBm differential power and the total integrated output noise is 208 $\mu V_{\mathrm{ rms}}$ . The total power consumption for the P-FFT filter bank (eight-channels total) is 34.6 mW (34.6 pJ/conv).

Fast Orthogonal Row-Column Electronic Scanning With Top-Orthogonal-to-Bottom Electrode Arrays.

Recently, top-orthogonal-to-bottom electrode 2-D arrays were introduced as a practical design for 3-D ultrasound imaging without requiring the wiring of a 2-D grid of elements. However, previously proposed imaging schemes suffered from speed or image-quality limitations. Here, we propose a new imaging scheme which we call Fast Orthogonal Row-Column Electronic Scanning (FORCES). This new approach takes advantage of bias sensitivity to enable high-quality and fast B-scan imaging. We compare this imaging scheme with an equivalent linear array, a previously proposed row-column imaging scheme, as well as with the Explososcan imaging scheme for 2-D arrays through simulations. In a point phantom simulation, the lateral (azimuthal) resolution of a 64 ×64 element 6.67-MHz λ /2-pitch array using the FORCES imaging scheme with an f-number of 1.7 was 0.52 mm with similar in-plane image quality to an equivalent linear array but with improved and electronically steerable elevational resolution. When compared with other 3-D imaging schemes in point phantom simulations, the FORCES imaging scheme showed an azimuthal resolution improvement of 54% compared with Explososcan. Compared with a previously introduced row-column method, the FORCES imaging scheme had similar resolution but a 25-dB decrease in sidelobe amplitude, significantly impacting contrast to noise in scattering phantoms.